The broad objectives of the proposed research are to gather further evidence for the identification of certain amino acids as neurotransmitters, and to examine pharmacological and physiological factors which influence their release. Emphasis will be placed on studies of endogenous amino acid release from different regions of the intact nervous system of the rat. We will study the conditions for release of gamma-aminobutyric acid and other amino acids from the intact spinal cord during perfusion of the spinal subarachnoid space, in response to stimulation of dorsal roots or exposure to depolarizing agents, uptake blocking agents, or receptor antagonists. Preliminary studies have shown that there is a steady release of amino acids from the retina into the perfused eye. It is anticipated that a system with excellent geometrical properties may be developed for study of the release of the putative retinal transmitters gamma-aminobutyric acid, taurine and glycine from the dark and light adapted retina and during perfusion with various pharmacological agents. Additional studies will examine the distribution and movement of amino acids in slices of central nervous tissue taken from animals treated with barbiturate anesthetic and anticonvulsant agents, or subjected to electroshock convulsions during life. We have found that certain barbiturates added in vitro block the K ion-depolarization induced release of gamma-aminobutyric acid from cortex slices. In the proposed studies, the barbiturates will be given in vivo to investigate if blockade of amino acid transmitter release plays a role in the mechanism of anesthetic action. The radioactive dansyl chloride method will be used for amino acid assay. This permits measurement of endogenous amino acids in microgram samples of tissue and biological fluids.